Question about suits?

I'm in graduate school now and started right after I got my BA, so I never took time off to get a "real" job. I am going to school in the NYC area and would like to take advantage of some decent opportunities in the city to make a few bucks, but I don't have many business clothes. I have lots of nice stuff, but I don't have a suit or pants to match, and I only have 2 old ties which I can't actually tie. The only thing I have going for me is a decent belt and some real nice kenneth cole dress shoes. I really feel like I can get a decent job in Manhattan, but I can't just show up to an interview in khakis and a dress shirt. Where is a cheap place to get suits that will make me look semi-decent? I don't have much money at all, but I don't want to go to walmart and get a horrific suit that will make me look like a fool. yes, they sell suits at walmart here lol. Also, how many suits do I need? I don't want to be the loser wearing the same suit every day...yuck!